Radiotracer studies

Horanyi G and Rizmayer E M 1984 Radiotracer study of anion adsorption at silver electrodes in acidic medium J. Electroanal. Chem. 176 339-48... 

The effect on the eyes was more noticeable. A single application of the solution mentioned above produced moderate redness and short and minor swelling of conjunctiva. Radiotracer studies with Hostapur SAS [102] revealed that after oral (up to 50 mg/kg) and dermal application on rats, the product and its metabolites were very quickly excreted either in completely oxidized form as carbon dioxide or in the urine and feces. Residues in organs and tissues after 7 days were well below 1 ppm. 

A variety of other techniques have been used to investigate ion transport in conducting polymers. The concentrations of ions in the polymer or the solution phase have been monitored by a variety of in situ and ex situ techniques,8 such as radiotracer studies,188 X-ray photoelectron spectroscopy (XPS),189 potentiometry,154 and Rutherford backscatter-ing.190 The probe-beam deflection method, in which changes in the density of the solution close to the polymer surface are monitored, provides valuable data on transient ion transport.191 Rotating-disk voltammetry, using an electroactive probe ion, provides very direct and reliable data, but its utility is very limited.156,19 193 Scanning electrochemical microscopy has also been used.194... 

Corrigan DS, Krauskopf EK, RiceLM, Wieckowski A, Weaver MJ. 1988. Adsorption of acetic acid at platinum and gold electrodes— A combined infrared spectroscopic and radiotracer study. J Phys Chem 92 1596-1601. 

Radiotracer Studies with the Mixtures of C Labeled n-Hexane with Nonradioactive I-Hexene and Cyclohexane 54)... 

Obviously, once the hexatriene stage is reached, its cis isomer very rapidly gives 1,3-cyclohexadiene (59). Radiotracer studies have confirmed this cyclization step 20). However, tra 5-l,3,5-hexatriene may also be produced with almost the same probability (Scheme I). We do not agree with Rozen-... 

Step 10 is a thermal cyclization reaction not requiring a catalyst. The participation of a radical intermediate in the rearrangement reaction was verified by radiotracer studies (94a). 

Stepwise Ce dehydrocyclization was observed over potassia-chromia-alumina as well as potassia-molybdena-alumina catalysts (9, 10). Higher operating temperatures (450°-500°C) of these catalysts facilitate the appearance of unsaturated intermediates in the gas phase. Radiotracer studies indicate a predominant Ce ring closure of C-labeled n-heptane over pure chromia (132,132a). 

Capsaicinoids are synthesized by the condensation of vanillylamine with a short chain branched fatty acyl CoA. A schematic of this pathway is presented in Fig. 8.4. Evidence to support this pathway includes radiotracer studies, determination of enzyme activities, and the abundance of intermediates as a function of fruit development [51, 52, 57-63], Differential expression approaches have been used to isolate cDNA forms of biosynthetic genes [64-66], As this approach worked to corroborate several steps on the pathway, Mazourek et al. [67] used Arabidopsis sequences to design primers to clone the missing steps from a cDNA library. They have expanded the schema to include the biosynthesis of the key precursors phenylalanine and leucine, valine and isoleucine. Prior to this study it was not clear how the vanillin was produced, and thus the identification of candidate transcripts on the lignin pathway for the conversion of coumarate to feruloyl-CoA and the subsequent conversion to vanillin provide key tools to further test this proposed pathway. 

S this question a radiotracer study using 00 was undertaken and the... 

Table III. CO-Radiotracer Study of the Ru/Rh/EtgN/HOAc System for the Hydrogenation of Carbon Monoxide ...

The original work on wet chemical functionalization of germanium was reported as early as 1962 by Cullen et al. (researchers in RCA labs) [105]. They exposed ethyl Grignard to a chloride-terminated Ge(lll) surface and used radiotracer studies with tritiated ethyl groups to show that ethylation of the surface occurs via formation of Ge—C bonds in a one-to-one ratio with surface atoms. Because the chlorination procedure used by the authors can lead to formation of mono-, di-, and trichloride species, there may be some uncertainty as to the Ge/C ratio. However, these surfaces did demonstrate hydrophobic behavior and stability in both atmosphere and aqueous solution. 

Fig. 6.26. Two electrode positions in a radiochemical technique. On the left, the electrode is lifted up for adsorbate equilibration and bulk counting rate measurement. On the right, the electrode is pressed down (squeezed) against the scintillator for surface counting rate measurement. (Reprinted with permission from M. E. Gamboa-Aldeco, K. Franaszczuk, and A. Wieckowski, Radiotracer Study of Electrode Surfaces, in Surface Imaging and Visualization, A. T. Hubbard, ed., Ch. 46, CRC Press, Boca Raton, FL, p. 635,1995, Fig. 46.4.)...

In a series of experiments carried out by Pines and coworkers,202 the intrinsic acidity of alumina was neutralized before use to avoid ionic-type skeletal isomerization. Radiotracer studies showed that toluene formed from [l-l4C]-heptane over chromia-alumina contained only 18-32% labeling in the methyl group, that is, less than 50% required by 1,6 carbon-carbon closure.204 This indicates that direct 1,6 carbon-carbon closure is not the only path of cyclization of /(-heptane. 

Aromatization, however, may also be envisaged as taking place via stepwise dehydrogenation of an unbranched hydrocarbon molecule followed by ring closure of the polyunsaturated intermediates. In fact, the formation of dienes was proved during the aromatization of C6 and C7 alkanes to the corresponding aromatics over monofunctional metal oxides and metal black, and bifunctional catalysts.307 308 Radiotracer studies even allowed the detection in very low concentration of hexatriene during the aromatization of n-hexane over Pt black.309 It was also proposed that aromatics are formed from the cis isomers, whereas trans isomers may be coke precursors.213 Direct experimental evidence has recently been... 

Perhaps the most significant of the numerous applications of radiotracers in chemistry has been the study of chemical reaction mechanisms. In fact, most of the proposed reaction mechanisms have been verified by means of a radiotracer study. One of the simplest mechanistic experiments using radiotracers is to test the equivalence of various atoms in molecules in chemical reactions. An example of this type of study is the work of Volpin et al. (1959) on the equivalence of the seven carbon atoms in the tropylium ring. Volpin et al. reacted labeled diazomethane with benzene and brominated the cyclohepatriene product to form a labeled tropylium bromide, as shown below ... 

An interesting set of radiotracer studies of the deposition of pesticides was made by Atkins and Eggleton (1971). The pesticides were labeled with 14C, which was assayed using liquid scintillation counting. Results of the study showed that direct... 

Radiochemistry is defined as the chemical study of radioactive elements, both natural and artificial, and their use in the study of chemical processes (Random House Dictionary, 1984). Operationally, radiochemistry is defined by the activities of radiochemists, that is, (a) nuclear analytical methods, (b) the application of radionuclides in areas outside of chemistry, such as medicine, (c) the physics and chemistry of the radioelements, (d) the physics and chemistry of high-activity-level matter, and (e) radiotracer studies. We have dealt with several of these topics in Chapters 4, 13, 15, and 16. In this chapter, we will discuss the basic principles behind radiochemical techniques and some details of their application. 

Salonen, K., R. I. Jones, H. De Haan, and M. James. 1994. Radiotracer study of phosphorus uptake by plankton and redistribution in the water column of a small humic lake. Limnology and Oceanography 39 69—83. 

Tripathi, P,, S. M., Tripathi, R., and Prasad, B. B. (1975). Radiotracer studies of adsorption of sulfate ions on ignited alumina. Proc. Indian Natl. Sci. Acad., Part B 41, 156-159. 

The RBLR moth utilizes a blend of seven acetate esters with the biosynthetic pathway shown in Figure 3.6. This pathway is similar to the one just described, except the All desaturase starts with 14 CoA as the substrate and produces both Z and E isomers of ll-14 CoA in about a 60/40 ratio (Wolf and Roelofs, 1987). Recent cloning of the All desaturase from RBLR females indicates that the expressed enzyme produces a ratio of Z/E of about 6/1 (Liu el al., 2002). However, the final ratio of Zll- to Ell-14 OAc is 92/8 (Miller and Roelofs, 1980). A selective increase in the Z isomer occurs within the biosynthetic pathway. Timed radiotracer studies using [l-14C]acetate indicated that once 14 CoA was biosynthesized, the subsequent steps of Al 1 desaturation, reduction, and acetylation to the acetate esters occurred in quick succession (Bjostad and Roelofs, 1984). As indicated in section 3.3.4., the acetykCoA fatty alcohol acetyltransferase shows specificity for the Z isomer (Jurenka and Roelofs, 1989). Selective acetylation of Zll-14 OH and production of >60 percent Zll-14 CoA indicates that these enzymes have the inherent specificity to produce the 92 8 ratio of the major pheromone components Zll- and Ell-14 OAc. Two minor pheromone components are produced by chain shortening Zll- and Ell-14 OAc. The ratio of Z9- to E9-... 

M. A. Purcell, Radiotracer Studies of Test-Fired Bullets (master s thesis, University of California, Irvine, 1976). 

Pt-Sn Pt-Re Pt-Pb Initial catalyst lifetime, A1203 support Hexane and heptane reforming. Radiotracer studies. 

Tajima, K. (1971) Radiotracer studies on adsorption of surface active substance at, aqueous surface. 

Refs. [i] Inzelt G (2005) / Solid State Electrochem 9 245 [ii] Horanyi G (1980) Electrochim Acta 25 45 [iii] Horanyi G (2004) In Horanyi G (ed) Radiotracer studies of interfaces. Elsevier, Amsterdam, chapters 1,2,4,6 [iv] Horanyi G (2002) State of art present knowledge and understanding. In Bard AJ, Stratmann M, Gileadi E, Urbakh M (eds) Thermodynamics and electrified interfaces. Encyclopedia of electrochemistry, vol. 1. Wiley-VCH, Weinheim, Chap. 3 [v] Horanyi G (1999) Radiotracer studies of adsorption/sorption phenomena at electrode surfaces. In Wieckowski A (ed) Interfacial electrochemistry. Marcel Dekker, New York, pp 477 [vi] Horanyi G, Inzelt G (1978) / Electroanal Chem 87 423 [vii] Horanyi G, Inzelt G, Szetey E (1977) / Electroanal Chem 81 395 [viii] Vertes G, Horanyi G (1974) / Electroanal Chem 52 47 [ix] Horanyi G (1994) Catal Today19 285 [x] Horanyi G (2003) Electrocatalysis - heterogeneous. In Horvath IT (ed) Encyclopedia of catalysis, vol. 3. Wiley Interscience, Hoboken, pp 115-155 [xi] Inzelt G, Horanyi G (2006) The nickel group (nickel, palladium, and platinum). In Bard AJ, Stratmann M, Scholz F, Pickett CJ (eds) Inorganic chemistry. Encyclopedia of electrochemistry, vol 7a. Wiley-VCH, Weinheim, chap. 18... 

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